<!doctype html> 
<html> 
<head> 
    <meta charset="utf-8"> 
    <title></title> 
</head>
<body>
<script type="text/javascript">
	
var json = {};
json.a = function(){
	this.b = 10;
};
alert(json.length); //报错
json.a();
alert(json.length); //10

</script>
</body>
</html>